Sauerbraten 

(Sour roasted beef)
Use for 4-6 servings:

1kg     piece of beef (e.g. from the upper back hip, no usual roast beef!)
1/4 l   vinegar from red whine or a mixture 50:50 red whine and vinegar
2 bay   leafs
2 tblsp whole black pepper
2 big   onions
1 big   carrot
200g    potatoes 
1/4 l   bouillon
2 tblsp crème fraiche (or sour cream)
salt, pepper, oil

Place meat in a high dish, fill with vinegar (or mixture)  until covered. Add bay leafs and pepper grains and place dish in the refrigerator. Leave there for 2-3 days, turn meat around at least once.

Get meat out of marinade and dry. Spice meat with pepper all around.
   

 Cut onions, carrots and potatoes in little cubes. Heat oil, place meat in it and roast until brown from all sides. Add onions until brown, too.

Salt the meat, add potatoes and carrots, then the bouillon, and, optionally, some more red whine (esp. if you used only vinegar before).  Add also a little of the marinade (without leafs and pepper).

Simmer for at least 1 1/2 hours on low heat in a closed pot, turn once. 

Get meat out of the pot and keep warm.
Puree the sauce, let reduce a little. Add crème fraiche or sour crème, add salt and pepper to your taste.

Cut meat into slices, serve.

Traditional side dishes are potatoes or Kloesse (dumplings),  and some vegetable like Rotkraut (that is hot red cabbage).

In some areas of Germany, they add raisins and sliced apples to the sauce
so that it gets a more sweet-and-sour taste.